1. Field of the Invention
The present invention relates to a ceramic capacitor and, in particular, to a ceramic capacitor mounted on a substrate with a pair of external electrodes therebetween, and an electronic component including the ceramic capacitor.
2. Description of the Related Art
In recent years, with increases in performance of mobile electronic apparatuses, such as cell phones and notebook personal computers, the performance of a CPU or the like mounted on such a mobile electronic apparatus has been increased. This has made it difficult to reduce power consumption. On the other hand, mobile electronic apparatuses have been strongly required to be driven by a battery for a longer time.
Accordingly, mobile electronic apparatuses have been strongly required to increase the conversion efficiency of the power supply unit thereof. As the power supply units of mobile electronic apparatuses, DC-DC converters having good conversion efficiency have been widely used. A DC-DC converter circuit uses capacitors at an input portion and an output portion thereof. The capacitor used at the input portion is intended to accumulate electric charge. Therefore, it is desirable that the capacitor at the input portion have a low equivalent series resistance (ESR) and a high capacitance. Also, the DC-DC converter unavoidably produces a ripple voltage on the operating principles thereof. The ripple voltage depends on the impedance of the capacitor at the output portion. In order to restrain the above-mentioned ripple voltage, it is desirable that the capacitor disposed at the output have a low equivalent series inductance (ESL) and a low ESR.
In recent years, with further downsizing of mobile electronic apparatuses, the power supply units thereof have been strongly required to be downsized as well. Accordingly, DC-DC converters often used as power supply units, and capacitors for use in DC-DC converters have been strongly required to be downsized as well. For this reason, ceramic capacitors have been widely used as capacitors that can realize a large capacitance, a low ESR, and a low ESL as well as can be downsized.
Incidentally, in a DC-DC converter, a direct-current voltage on which a ripple voltage, which is an alternating-current component, is superimposed is applied to a capacitor. For this reason, in a DC-DC converter using a multilayer ceramic capacitor, the multilayer ceramic capacitor produces vibration due to an electrostriction effect. When the multilayer ceramic capacitor produces vibration, the vibration propagates to a mount substrate on which the multilayer ceramic capacitor is mounted. As a result, the mount substrate produces vibration. When the vibration frequency of the mount substrate extends to an audible frequency range, the mount substrate emits audible sound. That is, a phenomenon called “substrate noise” occurs.
In order to restrain the above-mentioned substrate noise, various attempts have been made. For example, Japanese Unexamined Patent Application Publication No. 2004-288847 discloses a capacitor 100 shown in FIG. 18. As shown in FIG. 18, the capacitor 100 includes a capacitor body 101 in which multiple internal electrodes (not shown) are formed. A first terminal electrode 102 and a second terminal electrode 103 are formed on the end surfaces of the capacitor body 101. The capacitor 100 is mounted on a substrate 106 with a metal terminal 104 bonded to the first terminal electrode 102 and a metal terminal 105 bonded to the second terminal electrode 103 interposed between the capacitor 100 and substrate 106. In the capacitor 100, the width of an inner connecting portion 102a bonded to the first terminal electrode 102, of the metal terminal 104 and the width of an inner connecting portion 103a bonded to the second terminal electrode 103, of the metal terminal 105 are smaller than the width of the terminal electrode 102 and that of the second terminal electrode 103, respectively. According to Japanese Unexamined Patent Application Publication No. 2004-288847, the above-mentioned configuration can enhance the spring properties of the inner connecting portions 102a and 103a and thus restrain propagation of vibration from the capacitor 100 to the substrate 106, thereby restraining substrate noise.
However, when the inventors of the present application conducted specific research on this device, it turned out that the capacitor 100 could not sufficiently restrain propagation of vibration thereof to the substrate and therefore could not sufficiently restrain substrate noise.